The interfacial stability between the cathode and electrolyte is an essential issue in the development of high-energy-density and long-life lithium-ion batteries. The deterioration of capacity dominated by Mn dissolution makes LiMn2O4 a representative case for studying the evolution of interfaces. Here, we use the ab initio molecular dynamics (AIMD) method to simulate the interface reaction between the ethylene carbonate (EC) molecules and the (110) surface of completely delithiated LiMn2O4 where most severe Mn dissolution is observed in the experiment. It is found that the intrinsic oxygen loss on the surface will drive the initial migration of surface Mn atoms to the electrolyte while reducing them. The EC molecules will decompose after transferring electrons to the surface Mn atoms, and its decomposition products further promote the Mn dissolution. In addition, oxygen loss and EC decomposition are in a competitive relationship when transferring electrons to the surface Mn atoms. This work provides a complete picture of the step-by-step dissolution of Mn atoms along with the interfacial evolution in the spinel LiMn2O4 system and also provides a scope for the study of transition-metal dissolution in other cathode materials and electrolytes.